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How LandTrendr Works

Most points on the Earth's surface have a "life history" captured in images taken by the Landsat Thematic Mapper instruments. With LandTrendr, we use statistical algorithms to separate trends from noise, and thereby identify periods of stability and of change for every pixel (30 by 30 meters in size). This process of trajectory segmentation is the core of all our mapping. The trajectory segmentation phase is preceded by substantial "pre-processing" needed to ensure that the data are clean enough to discern trends, and is followed by several different types of "post-processing" that make the maps ultimately of interest to most users.

Above, we show trajectories for three pixels. Light brown lines show the original data from Landsat, while colored lines show how LandTrendr segmentation simplified those data. Sharp jumps correspond to forest harvest, while slow declines correspond to gradual regrowth after harvest. The features of the segments can be mapped to show when events happened, or how fast processes such as regrowth are occurring.